Multiple release of polyplexes of plasmids VEGF and bFGF from electrospun fibrous scaffolds towards regeneration of mature blood vessels.

Key challenges associated with the outcomes of vascular grafting (for example, to fully vascularize engineered tissues and promptly regenerate blood vessel substitutes) remain unsolved. The local availability of angiogenic growth factors is highly desirable for tissue regeneration, and plasmid loading in scaffolds represents a powerful alternative for local production of tissue-inductive factors. No attempt has been made so far to clarify the efficacy of electrospun fibers with the loading of multiple plasmids to promote tissue regeneration. In the present study, core-sheath electrospun fibers with the encapsulation of polyplexes of basic fibroblast growth factor-encoding plasmid (pbFGF) and vascular endothelial growth factor-encoding plasmid (pVEGF) were evaluated to promote the generation of mature blood vessels. In vitro release indicated a sustained release of pDNA for ∼4 weeks with as low as ∼10% initial burst release, and the release patterns from the single and twofold plasmid-loaded systems coincided. In vitro investigations on human umbilical vein endothelial cells showed that the sustained release of pDNA from fibrous mats promoted cell attachment and viability, cell transfection and protein expression, and extracellular secretion of collagen IV and laminin. The acceleration of angiogenesis was assessed in vivo after subcutaneous implantation of fibrous scaffolds, and the explants were evaluated after 1, 2 and 4 weeks' treatment by histological and immunohistochemical staining. Compared with pDNA polyplex infiltrated fibrous mats, the pDNA polyplex encapsulated fibers alleviated the inflammation reaction and enhanced the generation of microvessels. Although there was no significant difference in the total number of microvessels, the density of mature vessels was significantly enhanced by the combined treatment with both pbFGF and pVEGF compared with those incorporating individual pDNA. The integration of the core-sheath structure, DNA condensation and multiple delivery strategies provided a potential platform for scaffold fabrication to regenerate functional tissues.